The invention relates generally to semiconductor devices, and more particularly to interconnections within semiconductor circuits and methods of making the interconnections, including methods for fabricating copper interconnects.
Integrated circuits are interconnected networks of resistors, transistors and other electrical components that are generally formed on a silicon substrate or wafer with conductive, insulative and semiconductive materials. Fabricating integrated circuits involves forming electrical components at a number of layers and different locations. The various components are then wired or interconnected together to form a memory or other electric circuit. Typically, the components are connected together by interlayer contact openings or vias formed through a dielectric layer to an underlying component and by conductive lines formed in trenches in the dielectric layer that extend from the via to one or more other vias in the layer. The trenches and vias are typically filled with aluminum, tungsten, copper, gold, silver, polysilicon, or other suitable conductive material.
The never-ending miniaturization of integrated circuits (IC) is leading to denser and finer pitched chips with ever increasing speed and performance. In order to enhance the performance of advanced integrated circuits, the interconnect systems are gradually migrating from aluminum-based metallurgy to higher-conductivity and more electromigration-resistant copper.
Of the several schemes proposed for fabricating copper interconnects, the most promising method appears to be the damascene process. In a single damascene process, channels or trenches are etched into the dielectric layer, and a metal is deposited to fill the etched trenches forming an interconnect line. In a dual damascene process, both the via and trenches are etched in the dielectric layer overlying an underlying interconnect or trace. The desired metal is then deposited into the trenches and holes in one step to form a dual damascene structure. Chemical mechanical polishing (CMP) is used to remove the unwanted surface metal, while leaving the desired metal in the trenches and holes, thus forming in-laid interconnect lines and vias that are coupled to electrical components beneath the insulation layer. The CMP processing leaves a planarized surface for subsequent metallization to build multi-level interconnections.
The introduction of copper conductors in integrated circuits has received wide publicity. Copper interconnect is the most promising metallization scheme for future generation high-speed ULSI, primarily because of lower electrical resistivity (1.7 vs. 2.3 xcexcxcexa9cm) and more electro/stress-migration resistance than the conventional aluminum-based materials. Full, 6-level copper wiring has now been introduced in a sub-0.25 xcexcm CMOS ULSI technology. However, copper atoms can easily diffuse through most oxides into the devices in the underlying silicon substrate and act as recombination centers to spoil device performance. Copper also diffuses into commonly used dielectric materials (i.e., SiO2) and certain polymers, resulting in conductivity of these insulators and higher effective dielectric constants.
Based on the foregoing, a suitable diffusion barrier is needed in order to adopt copper interconnects for ULSI. A variety of barrier materials such as tantalum (Ta), tantalum silicon nitride (TaSiN), titanium nitride (TiN), tantalum nitride (TaN) and tungsten nitride (WN) have been investigated.
These barrier films are generally deposited by sputtering to a thickness range of 20 to 30 nm and higher. If the barrier thickness does not scale with the device (and wiring scaling), the impact on electrical resistance is significant. The resistance increase due to liner (diffusion barrier) thickness becomes substantial for line widths of approximately 0.2 xcexcm and below. It has been reported that a very thin ( less than 6 nm) tungsten silicon nitride (WSiN) layer formed by electron cyclotron resonance (ECR) plasma nitridation of sputtered WSi film prevented copper diffusion.
A barrier metal free copper damascene interconnection technology has been reported. The scheme involved formation of a thin barrier layer on the surface of silicon oxyfluoride (SiOF) film by ammonia (NH3) plasma treatment. The reflow of copper was then performed at 400xc2x0 C. in atmospheric gas composed of N2/H2.
It would be desirable to provide a process for the formation of conductive contacts and interconnect lines that eliminates the need for depositing a metal barrier diffusion layer and results in a conductive contact/interconnect that has a higher purity and a lower resistivity compared to prior art films and contact structures.
The present invention provides methods for forming conductive contacts in a semiconductor structure, and the conductive components formed by those methods. In particular, the method is used to fabricate copper contacts and interconnects in integrated circuits such as memory devices. The method can be used to form single or dual damascene copper interconnects and vias in the manufacture of integrated circuits.
The method of the invention involves forming a conductive component in a semiconductor device. In one embodiment, the method comprises providing a substrate with an overlying insulating layer that includes at least one opening formed therein. A non-metal barrier layer is formed over the insulating layer, including over the sidewalls and bottom portion or base of the opening, by exposing the insulating layer to a nitrogen-containing plasma, preferably ammonia (NH3), to transform the exposed surface of the insulating layer to the barrier layer, preferably to a thickness of about 5 nm to about 10 nm to prevent diffusion of the conductive material into the insulating layer. In a preferred embodiment, the insulating layer comprises silicon oxyfluoride (SiOF), and the barrier layer comprises silicon oxynitride (SiON). A conductive material (i.e., copper) is directionally deposited into the opening, preferably by ionized magnetron sputtering. To ensure filling of the opening, the conductive material is then reflowed at a temperature of less than about 400xc2x0 C., preferably at a temperature of about 300 to about 350xc2x0 C., in the presence of atomic hydrogen that is preferably generated using a microwave-excitation high density plasma system using a krypton/hydrogen plasma. After depositing the conductive layer, excess conductive material is removed, preferably by chemical-mechanical polishing, to form the conductive contact in the opening. The method is useful for forming a contact to a semiconductor component underlying the insulating layer on a substrate, for fabricating a semiconductor circuit and an integrated circuit.
In another embodiment, the method can be used to form a dual damascene conductive structure in a semiconductor device by providing a substrate comprising a semiconductor component and an insulating layer over the semiconductor component, and etching the insulating layer to form a channel corresponding to a trench along the insulating layer, and an opening extending from the trench to the semiconductor component. A non-metal barrier layer is formed over the insulating layer including the exposed surface of the channel and the opening, and a conductive material is deposited on the barrier layer by ionized magnetron sputtering to fill the channel and the opening to form dual damascene conductive structures in the insulating layer. The dual damascene structures resulting from the process comprise an interconnect line coupled to a conductive contact to the semiconductor component. The barrier layer prevents diffusion of the copper into the insulating layer
Another aspect is a semiconductor circuit resulting from the method of the invention. The semiconductor circuit comprises a semiconductor structure; an insulating layer formed over the semiconductor structure with an opening formed through the insulating layer to the semiconductor structure and/or a horizontal trench opening extending over the insulating layer; a non-metal-comprising barrier layer formed over the insulating layer including the surface of the contact opening and/or the trench opening, which prevents diffusion of a copper-comprising material into the insulating layer; and a conductive contact formed in the contact opening and/or the trench opening over the barrier layer, and coupled to the semiconductor structure. The conductive contact comprises copper sputtered into the contact opening and/or the trench opening and reflowed at a temperature less than about 400xc2x0 C. in the presence of atomic hydrogen.
In another embodiment, the semiconductor circuit comprises a semiconductor structure; an insulating layer formed over the semiconductor structure and having a plurality of generally vertical contact openings extending therethrough to contact locations on the semiconductor structure, and a plurality of generally horizontal trench openings extending over the insulating layer; each of the contact openings and trench openings having a non-metal barrier layer formed on a surface; a plurality of generally vertical conductive contacts formed through the contact openings and coupled to the semiconductor structure; and a plurality of generally horizontal conductive interconnect lines formed in the trench openings, each of the interconnect lines coupled to at least one generally vertical conductive contact. The conductive contacts and/or the interconnect lines comprise copper deposited by ionized sputtering into the contact opening or the trench opening over the barrier layer and reflowed at a temperature less than about 400xc2x0 C. in the presence of atomic hydrogen to fill the contact opening and/or the trench opening.
Another aspect is an integrated circuit memory or microprocessor resulting from the method of the invention. The integrated circuit memory or microprocessor comprises an array of memory and/or logic cells, internal circuitry, and conductive contacts and interconnects coupled to the memory or logic arrays and internal circuitry. The metal contacts and interconnects comprise a one or more generally horizontal conductive interconnect lines extending over an insulating layer overlying the memory array, and one or more generally vertical conductive contact, whereby each interconnect line is coupled to at least one generally vertical conductive contact. The conductive interconnect and/or the conductive contact comprises copper deposited by ionized sputtering over a non-metal-comprising barrier layer overlying the surface of a trench opening extending over the insulating layer and/or a contact opening extending vertically into the insulating layer The deposited copper is preferably reflowed at a temperature less than about 400xc2x0 C. in the presence of atomic hydrogen to fill the trench opening and/or the contact opening. Preferably, the metal contacts and interconnects are formed using a dual damascene process.
Advantageously, the present invention provides higher purity copper contacts and interconnects having a lower resistivity (greater conductivity) compared to prior art copper films and contact structures. The method advantageously eliminates void formation in sub-micron trenches and contact openings, and other high aspect ratio conductive features. The process also eliminates the need to form a separate diffusion barrier by transforming a portion of the insulating layer to form a diffusion barrier film or layer between the metal (copper) contact/interconnect and the insulating layer.